The ever expanding use of semiconductor light emitting devices has produced a highly competitive market for these devices. In this market, performance and price are often significant for providing product distinction among vendors. Accordingly, a common objective is to reduce the cost of production while providing equivalent or better performance from the light emitting device.
One technique for providing relatively inexpensive packaging of a light emitting element is to place the light emitting element in a frame with leadframe contacts that facilitate external connections to the light emitting element. An LED leadframe generally comprises a pair of conductors that are shaped to provide for external connections to the LED. A support frame may be molded about the leadframe such that the leadframe conductors provide conductive surfaces within the support frame to mount the LED, and conductive surfaces at the exterior of the support frame to mount the framed LED on a printed circuit board or other fixture.
USPA 2010/0207140, “COMPACT MOLDED LED MODULE”, published 19 Aug. 2010 for Serge L. Rudaz, Serge Bierhuizen, and Ashim S. Hague, and incorporated by reference herein, discloses an array of support frames within which light emitting devices are bonded to leadframe contacts within each support frame, as illustrated in FIGS. 7A-7B.
FIG. 7A illustrates two leadframes 16 within a molded frame array 40. Each leadframe 16 includes conductors 12 and 14. In this example a tub 10 is formed about each leadframe 16, and the conductors 12 and 14 of leadframe 16 are shaped to extend through the frame element 40 so as to provide contacts 12a, 14a within the tub 10 for mounting a light emitting device, and contacts 12b, 14b for subsequent mounting of the tub 10 with light emitting device onto a printed circuit board or other fixture. Although only two leadframes 16 and tubs 10 are illustrated, a molded frame array 40 may include hundreds of leadframes 16 and tubs 10.
FIG. 7B illustrates two light emitting modules 38. In this example embodiment, a light emitting device 20, which may be a thin-film device with minimal inherent structural support, is situated on a submount 30, which provides the necessary structural support to the light emitting device 20. Other devices, such as an ESD protection device 26 may also be situated on the submount 30. A protective coating 28 may be provided upon the submount 30. Conductors 24 through the submount 30 couple the light emitting device 20 to the contacts 12 and 14 in the leadframe 16.
The tub 10 may be subsequently filled with an encapsulant. Optionally, the encapsulant, or the protective coating 28, or the light emitting device 20, may include a wavelength conversion material, such as phosphor, that absorbs some or all of the emitted light and emits light at a different wavelength. The interior walls 15 of the tub 10 may be reflective, to redirect light toward the outside of the tub 10.
Upon completion, the individual light emitting modules 38 formed by the frame array 40 are singulated by slicing along the line 36. The individualized light emitting modules 38 include side surfaces 35 that facilitate the picking and placing of the light emitting module 38, but consume significantly more volume than the light-producing element 20, and introduces a substantially larger footprint compared to the surface area of the light-producing element 20. This substantial volume and footprint ‘overhead’ limits the use of such a light emitting module in applications such as flash or illumination elements for portable devices, such as smart phones and the like.